How to do bidirectional Replication in SQL Server 2005?

Greetings... Presently, I am doing one way replication in SQL Server 2005. Server-A is local server at local place and Server-B is remote server at different place. There is not a problem in one way replication. Server-A is Distributor and Server-B is Subscriber in one way replication. I want to setup the following configuration using bidirectional replication (two way replication) on SQL Server 2005 And I am not able to do it. What should I do for this? Should I use Merge Replication for bidirectional Replication. Server-B is live server for users which cannot be stop for a moment. Server-A is local server which is live too. Now please let me know how to do Bidirectional Replication. So whatever data in Server-B (Which is live) should replicate to Server-A or Vice versa ... If we add some column into Server-B's table of Database what could be the effect on Server-A... Please someone help me out into this. Thanks Ricky